Solid high energy borane fuel composition



United States Patent 3,128,212 SOLID HIGH ENERGY BORANE FUEL CUWQSI'IION Trescott B. Lat-char, Sr., Lewiston, Wallace R. Mitten, Grand Island, and Amanrlus D. Snyder and William K. Taft, Lewiston, N.Y., assignors to Olin Mathieson Chemical Corporation No Drawing. Filed July 18, 1958, Ser. No. 749,563 18 Claims. (Cl. 149-19) This invention relates to reaction products of polymers of the butadiene-n1ethylvinylpyridine type and boranes.

Polymers of the butadiene-methylvinylpyridine type are well known. The ones particularly useful in this invention are copolymers of butadiene and 2-methyl-5-vinylpyridine and terpolymers of butadiene, Z-rnethyl-S-vinylpyridine and acrylonitrile.

It has now been found that certain boranes can be combined with the butadiene-rnethylvinylpyridine polymers to form a solid material of high boron content suitable for use as a propellant fuel for rocket power plants and other jet propelled devices.

The fuels of this invention when incorporated with suitable oxidizers such as ammonium perchlorate, potassium perchlorate, sodium perchlorate, ammonium nitrate, etc., burn with high flame speeds, have high heats of combustion and are of the high specific impulse type. Probably the most single important factor in determining the performance of the propellant charge is the specific impulse. Appreciable increases in performance will result from the use of higher specific impulse materials.

The fuels of this invention when incorporated with oxidizers are capable of being formed into a wide variety of tablets, rings and shapes with all the desirable mechanical and chemical properties. Propellants produced by the method described in this application burn uniformly without disintegration when ignited by conventional means, such as pyrotechnic type igniter, and are mechanically strong enough to withstand ordinary handling.

One of the important advantages of the fuels of this invention is that some of them are elastic and hence resist cracking by heat and thermal shock. Solid propellants for jet propelled devices may be exposed to a variety of temperature conditions. Wide variations in the temperatures cause thermal expansions which may inducecracking in the propellant grains. Physical shocks which may be experienced by the propellant grains both before and during their discharge in jet propelled devices may also cause fracture and cracking in the grains. Such cracked propellant grains may be extremely dangerous to the jet propelled device in that they permit an uneven burning rate of the grain. This uneven burn-ing may cause a violent thrust in the jet engine or an explosion in the rocket power plant. It is therefore very essential that the propellant used not be subject to fracture. Compounds having a rubber-like quality are particularly desirable for use in propellant grains because they can absorb both thermal and mechanical shock without cracking or fracturing. The natural resiliency and elastic qualities of rubber-like materials make them ideal for resisting fracture. The fuel of this invention will not deteriorate when stored over a wide range of temperature conditions. it can be produced in a uniform composition, can easily be cast into grains, and will not shrink. In addition the high percentage of boron which is present in the propellant composition is readily burnable and results in the release of a much larger quantity of energy than the corresponding composition of carbon. The fuels of this invention need not use the conventional binding agent used by many other fuels to cause the oxidizer and fuel to adhere. The cohesive and tacky quality of the final product is ice sufficient to bind into a solid mass the granular oxidizing agent admixed with the fuel. Such mass will retain its form and elastic qualities when shaped into various configurations.

According to this invention, the butadiene-methylvinylpyridine polymer, is reacted with a borane to produce solid materials useful as propellant fuels.

The polymers suitable for use in this invention include particularly copolymers of butadiene and 2-methyl-5-vinylpyridine and terpolymers of butadiene, 2methyl-5- vinylpy-ridine and acrylonitrile. A particularly suitable product is a copolymer of butadiene and 25% 2- methyl-S-v-inylpyridine. This product is a solid and is known commercially as Philprene VP-25.

Property (-Philprene VP25): Value Apparent density, -g./cc 0.86 Gel, percent 0-5 D-ilute solution viscosity 1.89

Another particularly suitable product is a terpolymer of 70% butadiene, 10% 2-methyl-5-vinylpyridine and 20% :acrylonitrile. This product is a solid and is known commercially as Philprene VPA.

Property (Philprene VP-A): Value Apparent density, g./cc. 0.84 Gel, percent 05 Dilute solution viscosity 1.30

The butadiene-methylvinylpyridine polymers useful in this invention have an aver-age molecular weight in the range of about 20,000 to 500,000.

The boranes suitable for use in this invention include diborane, pentaborane, decaborane, lower alkyl pentaboranes in which the alkyl group contains from 1 to 5 carbon atoms and lower alkyl decaboranes in which the alkyl group contains from '1 to 5 carbon atoms. Such alkyl decaboranes include, for example, monomethyldecaborane, monoethyldecaborane, dimethyldecaborane, diethyldecaborane, triethyldecaborane and monoisopropyl decaborane. Mixtures of the boranes can be used. Lower alkyl pentaboranes can be prepared, for example, by reacting pentaborane-9 with an alkyl monohalide of 1 to 5 carbon atoms, e.g., methyl chloride, while the reactants are in admixture with an alkylation catalyst, e.g., aluminum trichloride, as described in pending application Serial No. 497,408, now Patent No. 3,038,012, filed March 28, 1955, of Altwicker et al. Alkyl decaboranes can be prepared by reacting decaborane and an alkyl halide in the presence of an alkylation catalyst .as described in pending application Serial No. 497,407, now Patent No. 2,999,117, filed March 28, 1955, of Altwicker et al., and in pending application Serial No. 540,141, filed October 12, 1955, now Patent No. 3,109,030, of Altwicker et al., wherein ferric chloride is used as the catalyst. Monoethyldecaborane can be also prepared by the reaction of decaborane and ethylene as described in pending application Serial No. 514,121, filed June 8, 1955, of Stan-ge et al. Also alkylated decaboranes such as monoethyldecaborane and diethyldecabor-ane can be prepared by reacting a monoolefin hydrocarbon with a mixture of decaborane and an aluminum halide as described in pending application Serial No. 557,634, new Patent No. 2,987,552., filed January 6, 1956, of Neil et al.

The polymer is generally reacted with the borane at temperatures ranging from about --l0 to 150 C., preferably about room temperature to C. and at pressures varying from 0.002 mm. of mercury to several, e.g., 3 to 5, atmospheres, although atmospheric pressure is preferred. The time of reaction varies from a few minutes to several hours, e.g., as high as 50 hours depending on the temperature pressure employed. The degree of completeness of the reaction can be determined by the rate and quantity of hydrogen evolution, as well as the gelation of the reaction mixture. The mixture can become gelled in seconds, while the evolution of hydrogen may continue for more than 20 hours. The ratio of reactants can be varied widely, generally being in the range of about 20 to 0.1 parts by weight, preferably about 11 to 1, of polymer per part by weight of borane.

Although the reaction between the polymer and borane will proceed in the absence of a solvent, best results are obtained, especially where solid or gaseous reactants are used such as decaborane (solid) or diborane (gas), by carrying out the reaction in a solvent common for but inert to the reactants. Such solvents include aliphatic hydrocarbon solvents such as n-pentane, hexane and heptane, aromatic hydrocarbon solvents such as benzene, toluene and xylene, cycloaliphatic solvents such as cyclo hexane and methylcyclopentane and oxygenated organic solvents such as tetrahydrofuran, ethyl acetate and diisopropylether. The amount of solvent can vary widely, but is generally within the range of about 1 to 100 parts by weight per part by weight of each reactant. Such solvents can be introduced into the reaction vessel with the reactants or the borane or polymer can be dissolved in the solvent and the solution introduced into the reaction vessel with the borane or polymer. Also, solid polymers, such as the VP-25 and VP-A described above, can be first plasticized to a liquid state before reaction with solid or gaseous boranes. Conventional plasticizers or the liquid boranes can be used.

The reaction product can be cured by carrying out the reaction under curing conditions of temperature and pressure or by first forming the reaction product and then curing it. Curing agents such as the boranes can be used as well as conventional cures applicable to the butadiene-me-thylvinylpyridine polymers, e.g., a sulfur cure. The curing agents can be present during the reaction or used in a later curing step after separate formation of the reaction product. The curing conditions vary with the particular polymer used and range in time from minutes to 3 hours or more and in temperature from about to 150 C.

For the preparation of propellant compositions containing an oxidizer, the oxidizer can be added to the reaction mixture, including the curing agent if it is present, and the reaction and curing carried out in the presence of the oxidizer; or the oxidizer can be added to the separately formed reaction product before curing; or the oxidizer can be added to the separately formed and cured reaction product, e.g., by mixing it into the product. The amount of oxidizer in the mixture can vary from about 5 to 95 percent.

The solid materials produced by the reaction described above are elastic or rubber-like to resinous solids of varying hardness and colors. Some are tacky. They are non-pyrophoric but burn readily on ignition. The solids contain substantial proportions of boron and the boron is linked to the polymer molecule, probably between two or more molecules.

The invention will be further illustrated by reference to the following examples.

EXAMPLE I 6.5 g. of VP-A (polymer VPA, is a terpolymer of 70/10/20 butadiene/2 methyl 5 vinylpyridine/acrylonitrile terpolymer) were dissolved in 65.5 g. of toluene, making a solution of 9 percent of VPA by weight. 20 g. of this solution was added to a reaction flask connected to a vacuum line. The system was flushed with nitrogen, and then 0.489 g. of diborane, mixed with nitrogen, was bubbled through the polymer solution over an interval of-5 minutes, at a temperature of 22 to 30 C. The weight ratio of polymer to borane was 3.7:1. As diborane was added, the material in the reaction flask became viscous, and finally had the appearance of a solid gel. After the diborane had been added, the nitrogen flow was continued, but at this point the inlet tube in the reaction flask became completely plugged and nitrogen was forced out through the bubble off. The reaction flask was flushed with nitrogen and evacuated twice.

There was 3 distinct phases in the flask: (1) the largest phase on the bottom, a liquid resembling the original solution, (2) a solid, gel-like material at the surface of the liquid phase, somewhat lighter in color than the original reddish brown solution and (3) white solid material which plugged the inlet tubes. The liquid and solid phases were not apparent until the flask was evacuated the first time; rather, the material seemed to be a solid mass. When the fiask was evacuated, gas bubbles were pulled out, and the liquid phase separated out and remained at the bottom. The flask was opened in a dry box and portions of the liquid lower layer and the gelled upper layer were analyzed. Infrared analysis of the liquid phase was practically identical to that of the original V P-A solution in toluene (which showed only one band due to the polymer, the remainder due to toluene), while that of the gelled layer contained a weak band in the B H region as well. A portion of the gelled layer was washed with toluene and dried at room temperature. The material was rubbery and somewhat hard, and a very tough rubbery film was formed on the inside of the drying flask. The dried sample was found by Parr bomb sodium peroxide fusion to contain 2.34; 2.02 percent boron, and by benzene solubility determinations to contain 72, 78 percent gel.

EXAMPLE II 3.86 g. of VP-25 (a 75/25 butadiene/Z-methyl-S- vinylpyridine copolymer) in toluene (37.7 g.) was made air-free by sweeping with nitrogen in a 250 ml. flask. Decaborane (1.295 g.) was added dry, the system was sealed, and gas measurement was begun. The weight ratio of polymer to borane was 3:1. A red color moved through the solution and the viscosity increased. Bubbles formed and gas was evolved. The whole mass gelled within 25 hours at 25 to 26 C. and atmospheric pressure. In 21 hours, 122 ml. of gas had formed, which was shown by mass spectrographic analysis to be nitrogen and hydrogen. The gelatinous product was washed with toluene three times, ground in a mortar and washed with pentane three times and dried in a vacuum at room temperature. The boron content of the dried solid was 10.85, 11.01 percent.

EXAMPLE III A solution of VP-A (terpolymer of butadiene, methylvinylpyridine and acrylonitrile, charge ratio 701020 parts by weight of respective monomers) in toluene (18.8 g.) containing 1.86 g. of VP-A was placed in a 250 ml. flask. Nitrogen was admitted and removed three times. The temperature of the surrounding water bath was 27 C. Decaborane (1.065 g.) was admitted through a funnel against a stream of nitrogen. The weight ratio of polymer to borane was 1.7:1. Reaction started immediately and gelation was complete in about 10 seconds. Volumetric apparatus was connected as rapidly as possible, but no readings could be taken before the reaction was well underway. The reaction charge became an orange red mass which began to bubble internally. In 17.3 hours 17 ml. of gas was evolved. The material formed was removed from the flask, washed three times with toluene, crushed and dried under vacuum at room temperature. A solid material (2.1 g.) with some rubbery properties was obtained. Some decaborane odor was present and the material was shown by Parr bomb peroxide fusion to contain 7.83, 8.20 percent boron. After six days, the solid was no longer rubbery, but hard and inelastic.

EXAMPLES 1v TO VI 98.7 g. of a toluene solution containing 4.93 g. of VP-25 (a 75/25 butadiene/Z-methyl-S-vinylpyridine copolymer) and 0.484 g. of monoethyldecaborane were brought together in a nitrogen swept flask at 25 C. and atmospheric pressure. Gelation was complete in minutes and a Very firm gel was formed which split open when gas bubbles formed. At to 24 C., 65 ml. of gas was measured after 23.5 hours. The gel was red in color and when washed with toluene and pentane 5.1 g. of solid containing 6.14, 6.17 percent boron and 97 percent insoluble gel was recovered.

Examples V and VI shown in Table 1 were performed in a similar manner.

Time of Reaction, Hrs Temperature, 0-- Gas Evolved, ml.-- Wash Solvent used, g

Product Weight, g Product Characteristics Insoluble Gel, Percent Boron Content, Percent Remarks a The product burned with a sputtering yellow flame when ignited. b The swell volume in benzene of these products increased as ethyl groups were added.

The ethyl decaboranes used in Examples IV to VI were obtained from a Friedel-Crafts reaction of decaborane-M (B H and an ethylhalide, in the presence of a ferric chloride catalyst. The product of this reaction consisted of a mixture of ethyldecaborane, diethyldecaborane and triethyldecaborane. These constituents were separated by a fractional distillation at reduced pressures. At a pressure of about 0.2 mm. of mercury, monoethyldecaborane boils at approximately C., diethyldecaborane at 45 C. and triethyldecaborane at 65 C. By this method of separation products were obtained having a purity of greater than 99 percent. The boron-containing solid materials of this invention can be employed as ingredients of solid propellant compositions in accordance with general procedures which are well understood in the art, since the solids are readily oxidized using conventional solid oxidizers, such as ammonium perchlorate, potassium perchlorate, sodium perchlorate, aluminum perchlorate, lithium perchlorate, ammonium nitrate and the like. In formulating a solid propellant composition employing one of the solid materials generally from 10 to parts by weight of the boron containing material and from 65 to 90 parts by weight of oxidizer such as ammonium perchlorate are present in the final propellant composition.

In the propellant, the oxidizer and the product of this invention are formulated by intimately admixing the oxidizer with the reactants, i.e., the polymer and borane, before reaction and curing so that the oxidizer and boroncontaining product form a homogeneous mass or by intimately admixing the oxidizer with the uncured or cured reaction product which has been prepared without oxidizer, e.g., by finely subdividing each of the materials separately and thereafter intimately admixing them. The purpose in doing this, as the art is aware, is to provide a proper burning characteristic in the final propellant. The subdividing of the boron-containing solid reaction product can be accomplished by means of con ventional equipment designed to reduce the size of resilient materials, e.g., rubber, such as devices which cut, chop or tear the feed material into a divided product, e.g., the well-known rotary knife cutters and granulators. The oxidizer can be reduced in size by conventional equipment, e.g., a hammer mill. The admixing of the finely divided reaction product and finely divided oxidizer can be accomplished by conventional mixing equipment employing rotating blades, e.g., kneaders or Baker- Perkins mixers.

In addition to the oxidizer and oxidizable material, the final propellant can contain an artificial binder. Although, in general, it is not necessary to use such a binder when the fuel of this invention is utilized, one can be employed to secure additional binding strength, or Where a propellant fuel of different physical characteristics is desired. A binder of anartificial resin type, generally containing urea-formaldehyde or phenol-formaldehyde, is particularly useful. The function of this resin is to give the propellant strength and at the same time improve its burning characteristics. In manufacturing a suitable propellant using a binder, the reaction product containing the oxidizer or proper proportions of finely divided oxidizer and finely divided boron-containing material containing no oxidizer are admixed witha high solids content solution of a partially condensed urea-formaldehyde or phenol-formaldehyde resin, the proportion being such that the amount of the resin is about from 5 to 10 percent by weight, based upon the weight of the oxidizer and the boron compound. The ingredients are thoroughly mixed with the simultaneous removal of the solvent, e.g., by use of a vacuum, and following this the solvent-free mixture is molded into the desired shape as by extrusion. Thereafter, the resin in the mixture can be cured, e.g., by heating at moderate temperatures, e.g., 200 C. Conventional and suitable methods of formulation of solvent propellant compositions are further described in US. Patent 2,622,277 of Bonnell and US. Patent 2,646,596 of Thomas.

When the final propellant is to be made without binder or binding agent, the technique is very similar. When the boron-containing product has been made without oxidizer the oxidizer and product are again formulated in intimate admixture with each other, as by subdividing each of the materials separately and the intimately admixing them. The result of this admixture is a homogeneous solid having strong cohesive qualities, which will retain its form well, and which can be formed into various shapes as by extrusion. The molding can be done in conventional equipment designed for this purpose such as hydraulic extnuders. The extruded propellant can then be cut into pieces and trimmed as desired.

The following examples illustrate the formulation of solid propellant compositions utilizing the solid boron containing reaction product of this invention which has been prepared without oxidizer.

Example VII The solid boron containing material of Example I in an amount of 2.0 pounds is finely divided to a size of about 50 microns in a rotary knife cutter. Ammonium perchlorate (6.0 pounds) oxidizer is finely divided to a size of about 1 to 50 microns in a hammer mill. The two finely divide-d materials are then introduced into at Baker- Perkins mixer and intimately admixed. The resulting homogeneous cohesive solid is molded and extruded and cut into cylindrical grains of about 2 inches in diameter and 8 inches in length. The resulting solid grains are an intimate admixture of solid fuel'and oxidizer.

Example VIII The solid boron containing material of Example I and ammonium perchlorate oxidizer in the amounts of Example VII are finely divided as in Example VII and are introduced into a Baker-Perkins mixer along with 1.0 pound of a solution of a phenol-formaldehyde resin in epichlorohydrin and the three components intimately admixed with the simultaneous removal of the solvent by means of a vacuum. The resulting solvent-free homogeneous solid is molded and extruded to -form grains as in Example VII. The grains are then heated in an oven to about 100 to 150 *C. for one hour to cure the resin in the grains. The resulting grains are an intimate admixture of solid fuel and oxidizer with resin binder.

The product of this invention can be utilized in its extracted form, that is after the uncombined borane has been removed from the final reaction product by extraction with a suitable solvent. The unextractcd reaction product, however, can be also advantageously used as a jet propellant. The unextracted product contains a quantity of borane homogeneously dispersed throughout. When combined with an oxidizer in the manner previously described and ignited, both the combined product and the borane burn readily. The unextracted product has the advantage of containing a higher percentage of boron (an element having a high heat of combustion) homogeneously dispersed in a form which can be easily admixed with a suitable oxidizing agent and which will burn liberating a larger quantity of energy than the extracted product.

What is claimed is:

1. A solid high energy fuel composition consisting essentially of the product of reaction of butadiene-methylvinylpyridine polymer and a borane selected from the group consisting of diborane, pentaborane, decaborane, lower alkyl pentaborane and lower alkyl decaborane and mixtures thereof at a temperature of about 10 to 150 C. and in amounts of about 20 to 0.1 parts by weight of polymer per part of borane.

2. A solid high energy fuel composition consisting essentially of the product of reaction of (1) a polymer selected from the group consisting of butadiene-Z-methyl- 5-vinylpyridine copolymer and butadiene-Z-methyl-S- vinylpyr-idine-acrylonitrile terpolymer and (2) a borane selected from the group consisting of diborane, pentaborane, decaborane, lower alkyl pentaborane and lower alkyl decaborane and mixtures thereof at a temperature of about to 150 C. and in amounts of about 20 to 0.1 parts by weight of polymer per part of borane.

3. The composition of claim 2 in which the polymer and borane are reacted in an amount of about 11 to 1 parts of polymer per part of borane at a temperature of about room temperature to 100 C.

4. The composition of claim 2 in which the polymer comprises about 75 butadiene and about 25 Z-methyl- 5-vinylpyridine and the borane is decaborane.

5. The composition of claim 2 in which the polymer comprises about 75% butadiene and about 25% Z-methyl- 5-vinylpyridine and the borane is monoethyldecaborane.

6. The composition of claim 2 in which the polymer comprises about 75 butadiene and about 25 Z-methyl- 5-vinylpyridine and the borane is diethyldecaborane.

7. The composition of claim 2 in which the polymer comprises about 75 butadiene and about 25 2-methyl- 5-vinylpyridine and the borane is triethyldecaborane.

8. The composition of claim 2 in which the polymer comprises about 70% butadiene, about 10% 2-methyl-5- vinylpyridine and about 20% acrylonitrile and the borane is diborane.

9. The composition of claim 2 in which the polymer comprises about 70% butadiene, about 10% 2-methy1-5- vinylpyridine and about 20% acrylonitrile and the borane is decaborane.

10. The method of preparing a solid high energy fuel composition which comprises reacting butadiene-methylvinylpyridine polymer and a borane selected from the group consisting of diborane, pentaborane, decaborane, lower alkyl pentaborane and lower alkyl decaborane and mixtures thereof at a temperature of about 10 to 150 C. and in amounts of about 20 to 0.1 parts by weight of polymer per part of borane.

11. The method of preparing a solid high energy tuel composition which comprises reacting (1) a polymer selected from the group consisting of butadiene-Z-methyl- S-Vinylpyridine copolymer and butadiene-2-methyl-5- vinylpyridine aerylonitrile terpolymer with (2) a borane selected from the group consisting of diborane, pentaborane, decaborane, lower alkyl pentaborane and lower alkyl decaborane at a temperature of about -10 to 150 C. and in amounts of about 20 to 0.1 parts by weight of polymer per part of borane.

12. The method of claim 11 in which the polymer and borane are reacted in amounts of about 11 to 1 parts of polymer per part of borane and at a temperature of about room temperature to 100 C.

13. The method of claim 12 in which the polymer comprises about butadiene and about 25 Z-methyl- 5-vinylpyridine and the borane is decaborane.

14. The method of claim 12 in which the polymer comprises about 75% butadiene and about 25% 2-methyl- S-Vinylpyridine and the borane is monoethyldecaborane.

15. The method of claim 12 in which the polymer comprises about 75% butadiene and about 25% Z-methyl- 5-vinylpyridine and the borane is diethyldecaborane.

16. The method of claim 12 in which the polymer comprises about 75 butadiene and about 25 Z-methyl- S-Vinylpyridine and the borane is triethyldecaborane.

17. The method of claim 12 in which the polymer comprises about 70% butadiene, about 10% 2-methyl-5- vinyl-pyridine and about 20% acrylonitrile and the borane is diborane.

18. The method of claim 12 in which the polymer comprises about 70% butadiene, about 10% Z-mcthyl-S- vinyl-pyridine and about 20% acrylonitrile and the borane is decaborane.

References Cited in the file of this patent UNITED STATES PATENTS 2,558,559 Hurd et a1. June 26, 1951 2,791,883 Moore et a1 May 14, 1957 2,877,504 Fox Mar. 17, 1959 OTHER REFERENCES Hurd: Chemistry of the Hydrides, New York, John Wiley and Sons, Inc., 1952, p. 94.

Butz: Aviation Week, vol. 67, July 15, 1957, p. 27.

Major: Chem. Engineering Progress, vol. 54, N0. 3, March 1958, pp. 49-54.

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1. A SOLID HIGH ENERGY FUEL COMPOSITION CONSISTING ESSENTIALLY OF THE PRODUCT OF REACTION OF BUTADIENE-METHYLVINYLPYRIDINE POLYMER AND A BORANE SELECTED FROM THE GROUP CONSISTING OF DIBORANE, PENTABORANE, DECABORANE, LOWER ALKYL PENTABORANE AND LOWER ALKYL DECABORANE AND MIXTURES THEREOF AT A TEMPERATURE OF ABOUT -10 TO 150* C. AND IN AMOUNTS OF ABOUT 20 TO 0.1 PARTS BY WEIGHT OF POLYMER PER PART OF BORANE. 